**Persistently Low Oil Pressure**
1. Incorrect oil quantity or quality. For example, too little oil in the oil pan, thinner, deteriorated, or with decreased viscosity; water or diesel fuel mixed in.
2. Severely worn oil pump, resulting in insufficient pump pressure.
3. Severely clogged oil strainer or filter, preventing oil from entering the main oil passage.
4. Uneven contact surface between the oil pump and the engine block, causing severe air intake.
5. Loose crankshaft journal centrifugal purification oil chamber plug, causing significant oil leakage.
**Sudden Drop in Oil Pressure to Zero**
1. Loose drain plug; broken oil pipe.
2. Loose return valve adjusting bolt, allowing oil to flow back to the oil pan.
3. Oil strainer filter screen suddenly clogged with foreign objects, preventing oil from entering the main oil passage. 4. The connection between the camshaft and the oil pump is broken, causing the oil pump to partially rotate.
5. The oil pressure gauge suddenly malfunctions.
Oil pressure drops after engine temperature rises.
When a diesel engine is first started, the oil pressure is normal. As the engine temperature rises, the oil pressure gradually decreases. The main reason is that as the engine temperature rises, the oil viscosity decreases, increasing leakage losses in the lubrication system. This can occur if the oil is of a deteriorated or incompatible grade, or if the crankshaft clearance is too large.
Lower oil pressure at higher engine speeds.
1. Especially in diesel engines that have undergone major repairs, there may be washing cloths, paper scraps, lint, and gelatinous impurities remaining in the oil pan. When the engine is idling, the oil vacuum is low, and these impurities are suspended at the bottom of the oil pan, allowing for normal oil supply. As the engine speed increases, the oil pump's vacuum increases, drawing these impurities onto the oil filter, clogging it and preventing oil supply, resulting in a drop in oil pressure. 1. After reducing the throttle, the oil pump suction decreases, and impurities fall under their own weight, remaining suspended in the oil. Supply returns to normal, and oil pressure rises again.
2. The pressure regulating valve or filler valve spring is broken or lacks sufficient elasticity. When the throttle is increased, the ball valve opens to release pressure, but the spring cannot return the ball valve to its original position after the oil pressure drops, causing a continuous decrease in oil pressure.
Large fluctuations in oil pressure:
1. Air is drawn into the oil pump.
2. The pressure regulating valve or return valve spring is stuck by foreign objects, or the spring is bent and rubbing against the seat, obstructing spring movement and making it difficult to open and close the ball valve.
